I also love my Ross MkIII! I found it at a gun show in December for a measly $150. It's absolutely mint with sight hood and full length barrel but it has a cut back stock. After getting it I looked at as many pictures of WW1 sniper pictures. I beleave that mine is a "factory stripped" Ross which is something they did at the field armory. Unfortunately it's been sanded so the only thing that's left is the serial numbers which read "930 RS 1915".
How does it shoot? It's better then I am, I often just aim and shoot a group and then look at the spotting scope after and then giggle! it often puts 2-3 touching like a clover leaf and then a flyer 1" away! It shoots 2 moa or better with any factory ammo I feed it! Reloads are slowly cutting that in half.
Soon I'm going to do a shoot out between my MkIII Ross and my AG Parker long branch just to see which will win. I have a feeling it will be close! Pretty good considering the Ross is from 1915 and the AG Parker was assembled some time after the 1955 barrel manufacture date!